Bacterial Diseases

1. Bacterial Diseases • Enteric redmouth - ERM (Yersinia ruckeri) • Furunculosis (Aeromonas salmonicida) • Coldwater disease – CWD (Flavobacterium psychrophilum) • Bacterial gill disease (Flavobacterium branchiophila) • Bacterial kidney disease (Renibacterium salmoninarum) • Strawberry disease

2. Yersinia ruckeri • Enteric Redmouth Disease (ERM) • “Hagerman Redmouth” primarily RBT • Rucker - First reported in 1958 in Hagerman Valley. Named in 1978 Yersinia ruckeri

3. Host Range and Vectors • North American outbreaks – possibly due to carrier fish or contaminated eggs from Idaho • Sources - imported baitfish, ornamentals, bird feces, etc.

4. Clinical Signs ERM • Chronic: • Reddening in mouth and under operculum, and internally throughout peritoneum, intestine, and fat of the body

5. Y. ruckeri • Obligate parasite • Generally occurs 13° - 15°C • Acute, sub acute, chronic forms

6. Yersinia ruckeri • Non-spore forming, straight rod • Motile with flagella • No pigment, grows slowly at 8 and 35.

7. Carrier State • Intestinal shedding of organism • Stress conditions, carriers transmitted Y.r. to healthy fish but unstressed fish did not

8. Virulence of Y.r. • Strain typing has been done widely (Hagerman – Type I)

9. Treatment and control Vaccines: • First were Ross and Klontz 1965. JFRBC 22:713-719. phenol killed (in feed) • First commercial fish vaccine: licensed by USDA in 1976 (formalin-killed whole cells) • Single most effective management tool for control of mortality due to ERM.

10. Coldwater DiseaseFlavobacterium psychrophilium • Bacterial cold-water disease - CWD • First observed in Leetown WV in rainbow (peduncle disease) • Next in 1948 in Washington - lesions near tail, and on dorsum

11. Host Range and Vectors • Serious infections in salmonids worldwide - distributed widely across NA continent • Has been linked to viral pathogens such as IHNV

12. Host Range and Vectors • Free-living examples exist • Resident salmonids likely carriers

13. Clinical Signs CWD • Externally: rough appearance of skin and necrosis of fins • May see open ulcerations on skin • External or septicemic

14. Clinical Signs CWD • Internally: • Erratic/spiral swimming • Development of deformities and/or nervous disorders

15. Transmission • Natural reservoirs uncertain • Mortalities increase when IHN involved • Number one concern in Hagerman Valley

16. Diagnosis of CWD • From clinical signs and necropsy • Gram negative, Rods • Gliding motility • Growth best on low nutrient media

17. Treatment and control • Extra-label use of antibiotics for control – somewhat effective (but resistance a potential problem) • Vaccines

18. Furunculosis • One of the oldest known bacterial fish pathogens • Mostly associated with salmonids, but other fish can be infected • Obligate pathogen (fish to fish transmission)

19. Clinical signs • Acute - Adult, sub-adult, darken, stop feeding, hemorrhage base fins, internal hemorrhages • Fingerlings - dark, dying

20. Clinical signs • Chronic, focal dermal necrosis – BOILS • Acute septicemia

21. Transmission • Horizontal • Dead fish/fecal material • Mucus - asymptomatic carriers • Sediments and associated biota

22. Presumptive Diagnosis • Morphology, Stain, non-motile • Non spore-forming rod (1 x 2 µm) • Pigment forming non-motile

23. Treatment and control • Antibiotics: • Resistance can be a problem • Vaccines:

24. Bacterial/environmental Gill Disease (Flavobacterium branchiophilum) • Gill infections primarily in juvenile fish • F. branchiophilum dominant bacterial species • Found throughout North America and other countries

25. Clinical signs BGD • Flared gills, lethargy, swim high in water column • Gill lamellae fused/clubbed (poor oxygen transport) • Debris and bacteria present • Usually associated with poor environmental conditions or parasitic infestation

26. Diagnosis/control Diagnosis: • Usually based on clinical signs (obvious) • Test for specific bacteria Control: • Improve environmental conditions (increase DO) • Treat fish (various chemicals), 1-5% NaCl may be method of choice

27. Bacterial Kidney Disease Renibacterium salmoninarum • Initially described in Atlantic salmon (Scotland 1930) • Hatchery and wild salmonids • Global maybe except Australia, NZ ?

28. Clinical signs • Systemic infection slowly progressive • Acute and chronic forms • External: exophthalmia, blood filled blisters • on skin, pale gills, etc. • Internal: multifocal grey-white nodules on • kidney and other organs, cloudy fluid in body • Cavity, cystic cavities in skeletal muscle, etc.

29. Diagnosis • Gram Positive Fish Pathogen • 0.5 X 1 µm pairs or short chains • Requires L-cystein • Serum or blood enhances growth • Slow growing - 20 - 60 d • Survives inside phagocytic cells • FAT/ELISA • Clinical signs/exam

30. Control/treatment • Erythromycin (injection of adults) • Reduce loads and transmission • In feed • Expensive and not approved for food fish • No vaccines available • Avoid infection

31. Disease of unknown etiology • Strawberry disease • Symptoms • Reddened raised inflammation on skin • Morbidity 10-15% • Market size fish affected • Cause • Bacterial (?) • Allergic reaction (?) • Treatment • Antibiotics (withdrawal period)